While working on a case, I found out there is a little information about the fracture characteristics of car's windshield hit by a 5.56x45 mm bullet (.223 Rem). Looking through literature, I only found references to tests with handgun ammunition1 and to those referring to trajectory reconstruction2 and to the effect of glass fragments on a possible "target" sitting inside a car. Approaching three different instructors of shooting scene reconstruction courses, with a request for photos of 5.56 mm bullet impact on car's windshield, yielded the following answers: - They don't have such photos, as they don't practice with this caliber in their courses. - They don't have a definite answer why they don't use this caliber to shoot at car's windshields. As a result, I decided to conduct the test by my self and I think I have the answer to the question: "Why don't they?" The results show some differences between the impact characteristics of handgun ammunition (Low speed, large diameter) and rifle ammunition (High speed, small diameter)
Introduction
I received a case where a man was charged with attempted murder, after he fired at least 24 rounds of 5.56x45 mm (.223 Rem) from a M-16 assault rifle (AR-15), toward another man who set in his car. 24 cartridges of 5.56x45 mm were recovered from the scene but the crime scene investigator (CSI) could not find even one bullet! However, in the photos he took you could see bullet holes at the front bottom of the car, near and in the license plate (Pic. 1), two impacts on the hood (Pic. 2) and one impact on the windshield, in front of the driver's seat. (Pic. 3) The driver, who got injured, was rushed to a hospital where he was diagnosed with wounds from glass debris, no bullet was found inside the car! When I looked at the shape of the impact on the glass, I knew it was not a direct hit and it was most probably the result of a ricochet, but because the CSI did not measured angles and did not try to reconstruct the path of that bullet, I could not determine whether the ricochet came from the asphalt road or from the car's hood. In the shooting scene reconstruction course I participated, we only fired hand gun bullets to car's windshield, so I tried to look for data of penetration patterns from 5.56x45 mm bullets in literature and from three instructors of shooting scene reconstruction courses, but I could not find any viable data, i.e., photos of fracture characteristics of 5.56x45 mm bullet hitting a car windshield. Even though I managed to prove that the glass impact resulted from a ricochet, by comparing it to similar fracture characteristics of 9x19 mm bullet, I thought it is a good time to conduct a shooting test and to find out what are the actual fracture characteristics of 5.56x45 mm bullet hitting a car windshield.
The Test Procedure
I purchased a windshield of Audi A6, which was a little fractured and not suitable to be installed back on a car and I took it to an open-air range who also have a weapon in 5.56x45 mm caliber, it is the EMTAN model MZ-4 14.5F. (Pic. 4) {14.5 is the length of the barrel} The muzzle velocity is around 875 m/s (2,870 ft/s). A "witness" cardboard was placed behind the windshield, in order to capture the impact of the glass fragments, from the internal layer of glass, on potential target siting inside a car. A single shot was fired almost orthogonally at an intact part of the windshield from a distance of 15 meters (50 feet), due to safety regulations. The impact hole was examined, photo'd (Pic. 5), marked number 1 and also was tested with the Bullet Test Kit (BTK), which gives reaction to the presence of Copper and Lead. A second shot was fired also orthogonally and hit under the bullet hole of the first shot. This impact hole was also examined, photo'd (Pic. 6), marked number 2 and also was tested with BTK. The last and third shot was fired at a very shallow angle, almost tangent to the surface of the windshield, which is a little curved. It was also examined, photo'd (Pic. 7), marked number 3 and also was tested with BTK. The reason for the BTK testing was to see if there are differences in reactions between penetrating bullets and skimming bullets.
Results and comparison to 9x19 mm bullet impacts
The first bullet created a round hole in the first layer of the laminated glass, approximately 7 mm in diameter, and a hole in the inner polymer sheet, approximately 3 mm in diameter. (Pic. 8) It is interesting to see that the typical "spider web" fractures, usually seen in bullet holes made by hand guns, for example 9x19 mm FMJ (Pic. 9), are almost missing. There are only two long lines of fracture, in diagonal, from two sides of the bullet hole. (Pic. 10) This might be the reason why high speed, small caliber ammunition is not used, because the instructors want to demonstrate to their students the whole range of fracture characteristics and it is harder to obtain it in those calibers. The second bullet produced similar characteristics to those of the first one, the same dimensions of the holes, in the outer and inner layers, and almost no "spider web" lines. The reactions of the BTK from those two bullet holes, to the presence of residual Copper and/or Lead, were minimal to nothing! The third shot left a typical "egg" like shape, with the wider part at the beginning of the impact trail, and an elongated hole, measured 13 mm in length and 5 mm in width. (Pic. 11) This hole gave a very strong reaction to the presence of residual Lead and weak reaction to the presence of copper. When comparing the characteristics of the impact on the windshield of the car from the scene (Pic. 3) to those of bullet number 3 from the test, one can see a remarkable resemblance. (Pic. 12)On both first shots, the glass fragments created holes in the witness cardboard measuring 12x20mm (app. 0.5x0.8 inch), where 12 mm is the vertical dimension and 20 mm is the horizontal dimension. (Pic. 13)
Discussion and points to future tests
There are clear differences between the impact characteristics of high velocity (875 m/s), small caliber, bullets to those of low velocity (300 m/s), bigger caliber bullets, fired at windshield glass of a car, not only in the dimensions of the hole but also in the fracture's characteristics. It can be determined that a bullet fired at sharp, tangent, angle, will live similar fracture marks resembling to those of a ricocheted bullet. The fact that the "ricochet" impact responded to the BTK, can also be used a tool to prove that a certain impact is from a ricochet and not from a direct hit! It would be interesting to learn what would be the impact characteristics of 5.56x45 mm bullet hitting a windshield at a velocity close to the one of a 9x19 mm bullet. It can be achieved in two ways:
Shooting from a long distance.
Lowering the amount of gun powder in the cartridge by emptying and reloading it.
Unfortunately, I don't have the possibility to do either of the above, so I hope someone who can will take this test further.
References
William W. Harper, "Behavior of Bullets Fired Through Glass", The Journal of Criminal Law & Criminology, Vol. 29, Winter 1939, PP718-723.
Duncan MacPherson et al., "Windshield Glass Penetration", Journal of the International Wound Ballistics Association, Vol.2 No. 4 1996, PP35-39.
Constantin Lux et al., "Gunshots through laminated glass: expelled compounded fragments as a function of bullet type", International Journal of Legal Medicine, November 2022, PP1235-1244.
Michael G. Haag, "Asymmetrically-Positioned Concentric and Radial Cracks at Shallow-Angle Glass Impact Sites for Determination of Projectile Direction of Travel", AFTE Journal, 2016 Volume 48, Number 3 (Summer), Page 173 thru 177.
Michael Van Arsdale et al., "Determining Bullet Trajectory from a Ricochet Off Windshield Glass", AFTE Journal, 1998 Volume 30, Number 2 (Spring), Page 309 thru 315.
Garry A. Rathman et al., "Bullet Impact Damage and Trajectory Through Auto Glass", AFTE Journal, 1993 Volume 25, Number 2 (Spring), Page 79 thru 86.
